The making of modern fabrics is an intricate and complex process. Success in the textile field does not just happen. It is the result of much thought and much planning. It is the end product of an ability to bring into focus a body of knowledge which involves the proper use of men, material, and machinery. Of all the decisions made in a textile operation none is more important than the decision of how, and with what, is the warp sizing done.
Warp sizing is the process of giving a protective coating on the warp yarn to minimize yarn breakages during weaving operation.
Sizing the warp is science versus art. Despite a high degree of sophistication in the chemical and physical sciences as they apply to textile sizing, and despite great strides in the development of mechanical, computer and electronic equipment and control for slashing, the process is not an exact science. Rather it is an art which relies on a mixture of science, technology, experience, and experimentation
Sizing operation is to produce weavability in the warp. This short description relates to a rather complex process to obtain the desired results.
A very important point to make is that errors in warp sizing can have a disastrous effect in the weaving room and in the finishing department and thus on the final product.
In order to obtain a good weavability, the yarn should be made capable of withstanding the forces during the weaving process without being damaged or becoming (extremely) hairy. The elasticity of the sized yarn should be high enough and the flexibility of the yarn should be sufficient to withstand these forces and movements. The size plays an important part in obtaining these results; the principal actions of the sizing are
- Protruding fibers should stick to the yarn body (decrease hairiness)
- Tying fibers so that they are fixed in the yarn body, in order to prevent protruding fibers being disrupted.
- Giving a sized film on the circumference of the yarn body (protection of the yarn).
- Making thin places stronger.
- Making thick places (with a relatively low twist) stronger.
- To reduce electrostatic formation for synthetic or blended yarns.
Benefits of Sizing
- It prevents the warp yarn breakage due to abrasion with neighboring yarns or with backrest, heald eye and reed.
- It improves the yarn strength by 10 to 20%, although it is not the primary objective of sizing process.
Characteristics of Sized Yarn expected by management
- Higher strength
- Lower elongation loss
- Higher bending rigidity
- Higher abrasion resistance
- Lower hairiness
- Lower frictional resistance
- Creep factor affecting elongation and elasticity of yarns
The performance of the yarn in weaving improves as the size add-on increases. The optimum add-on level is marked by a very low level of warp breakage rate. However, if the size add-on is higher than the optimum level then warp breakage rate increases again largely due to the loss of elongation and increase in bending rigidity of the yarns.
The optimum level of size add-on will depend on the following factors:
- Type of fiber
- Type of size materials
- Yarn spinning technology
- Yarn count and twist
- Level of hairiness in the yarn
- Loom type and loom speed
Although add-on primarily influences the weaving performance, it is possible to have different weaving performances even at the same level of size add-on. This can happen due to differences in (a) Size penetration and (b) Size coating or encapsulation
After meeting the requirements for a perfect size formula in terms of sizing efficiency, there are other considerations which must then be weighed. These considerations must be met by answering following questions
- Will the material be available in uniform grades? If not, there will be trouble ahead when results vary from one batch to another.
- Will the material be available when needed and insufficient quality?
- Will the cost of the material be prohibitive? The price of material is itself is not the whole consideration. A high-priced material size may be worth the difference in results when compared with a cheaper formula which causes frequent loom stoppages or ruined cloth.
- Will the material be compatible with other materials being used?
Only after the above questions are answered can a sound decision be made regarding the selection of a size.
- The various properties which can be readily compared to known test methods and definitely have an effect on weave ability of the yarn are 1. Abrasion resistance under tension (test both yarns against yarn and yarn against metal)
- Increase in tensile strength.
- The minimum loss of elasticity.
- Smoothness of film
- Shock resistance, ability to withstand repeated strains
- Resistance to the cutting of adjacent ends by knots and gouts.
- Fiber laying
- Film hardness.
- Sensitivity to changes in relative humidity.
- Resistance to shedding.
- Film strength
- Adhesion to yarns.
- Residual elongation.
- Reduction of friction
These tests can give only some indication of what to expect in the weave room an indication is better than nothing, and often the reason why a warp is running improperly can be determined by such tests
Evaluation of sizing in the weave room
- Production efficiency
- Loom stoppages from warp defects
- Cloth quality
- Cloth appearance and hand
- Shedding of size
- Shedding of lint.